Granule cracking in bio-organic fertilizer production lines is primarily caused by excessive moisture gradients between the granule's interior and exterior, rapid temperature rises, improper hot air velocity, and insufficient granule strength. Optimization can be achieved simultaneously across four areas: granulation pre-treatment, drying temperature control, equipment adjustment, and staged processing.

I. Strictly control moisture content at the granulation outlet and minimize moisture gradients. The moisture content of wet granules should be maintained between 26% and 30%. If moisture is too high, the surface loses water and shrinks rapidly during drying, while internal moisture vaporizes and expands, causing the granules to crack; if moisture is too low, the granules lack structural integrity and are prone to breaking during transport and drying. During granulation, appropriate binders—such as bentonite, humic acid, or starch—should be added to enhance granule density and toughness, thereby reducing the likelihood of cracking during drying. Fines and broken fragments generated during extrusion or disc granulation should be fully recycled for reprocessing to prevent loose, substandard particles from entering the biology organic fertilizer dryer.

II. Employ staged, low-temperature drying to avoid sudden heating and rapid dehydration. Direct contact between high-temperature hot air and wet granules is strictly prohibited. The dryer should utilize a three-stage temperature control system: an inlet pre-drying zone (60–80°C) to slowly remove surface free water; a middle main drying zone (80–100°C) to remove internal bound water; and an outlet cooling zone (below 50°C) to gradually dissipate residual heat. The temperature should not exceed 110°C at any stage, as excessive heat causes cracking and destroys beneficial biological bacteria. A gradual heating approach minimizes the moisture differential between the granule's interior and exterior, allowing moisture to release at a steady rate and preventing the outer shell from rupturing due to the rapid expansion of internal water vapor.

III. Adjust hot air velocity and drum rotation speed. Hot air velocity should not be excessive; strong airflow can rapidly dry the granule surface, forming a hard shell that traps internal moisture and leads to surface cracking or hollow granules. Moderately reduce the induced draft fan's airflow to ensure the hot air penetrates the material layer gently. Simultaneously, the rotational speed of the dryer drum is adjusted to extend the residence time of the pellets, allowing for slow drying that ensures moisture dissipates evenly; internal lifting flights are fitted with buffering and flow-guiding features to minimize damage caused by high-drop impacts and reduce physical breakage.

IV. Optimization of Cooling and Raw Material Preparation: Pellets must not be bagged immediately after drying; they require thorough cooling to room temperature before screening and packaging, as rapid contraction caused by exposing hot pellets to cold air can lead to widespread cracking. Raw materials are ground to the required fineness—with coarse fibers sufficiently refined—to ensure a dense pellet structure; material distribution at the dryer inlet is kept uniform to prevent localized areas from becoming either too thick (resulting in incomplete drying) or excessively dry (leading to cracking). Accumulated material clumps inside the drum are cleared regularly to prevent large masses from obstructing hot airflow, which would otherwise cause uneven drying and result in batches of defective, cracked pellets.